In focusing or zooming of image pickup lenses in a known camera, a group of lenses is usually moved by driving a lens barrel with a motor and a series of gears connected with the motor. On the other hand, cameras are presented which move a group of lenses by the use of a shape memory alloy element, thereby achieving a space saving in a camera, instead of using a motor and a series of gears connected with the motor to move the group of lenses.
As a driving device using a shape memory alloy element, as described above, there are disclosed driving devices which have a detecting means for detecting the position of a driven object and control driving of the shape memory alloy element, based on information by the detecting means, and there are also disclosed driving devices which divide a shape memory alloy element in a string form in the longitudinal direction and individually control the divided elements to perform the position control of a driven object (for example, Patent Document 1).
Further, a driving mechanism is disclosed which uses a shape memory alloy element in a string form, making it into a dogleg shape, wherein the alloy element contacts with a driven object at the approximate central portion of the alloy element and is fixed at the both ends (for example, Patent Document 2).
[Patent Document 1] TOKKAI No. H10-307628
[Patent Document 2] TOKKAI No. 2002-99019
In recent years, a small and thin image-pickup unit is mounted on a portable phone or a small and thin electronic device, such as a PDA, realizing transmission of image information as well as audio information to and from a remote site.
As such portable terminals are used increasingly, with respect to image-pickup units to be built in a portable terminal, those which move a lens group to have not only a macro function but also an AF function and optical zooming function are coming to be mounted so as to obtain images in a higher image quality.
However, an image-pickup unit to be built in a portable terminal is required to be extremely small sized, for example, to have a volume of 1 cm3 or smaller.
With such a requirement, although a driving device, disclosed in above Patent Document 1, having means for position detection of a driven object has the advantage of accurate position control of the driven object, it has the drawback of requiring a space for the detecting means when it is applied to an image-pickup unit to be built in a portable terminal, and accordingly the image-pickup unit becomes large. Further, a driving device, which has shape memory alloy element divided along the longitude direction and performs individual control of the divided shape memory alloy elements, has a complicated circuit configuration for control, and the shape memory alloy elements are linearly disposed, which does not allow the device to be small.
Further, a unit, disclosed in above Patent Document 2, which uses string formed memory alloy elements formed in a dogleg shape has not a significant problem in being built in a large device, such as binoculars. However, fixing portions at both ends stick out much on the both sides of a driven object, which requires a solution to be applied to a small sized image-pickup unit to be built in a portable terminal. Still further, the unit, disclosed in above Patent Document 2, which uses string formed shape memory alloy elements also includes position-detecting means. As it is difficult to perform accurate position control without the detecting means, the unit also has a drawback of making the image-pickup unit large.
Yet further, if it is attempted to move a lens group by the use of a shape memory alloy element in an image-pickup unit built in a small sized portable terminal as described above, there is no space for detecting means, for position detection of the lens group, to be built in. Yet further, if there is variation in the lengths of built-in shape memory alloy elements, the variation causes a problem of variation in shrinking amounts and variation in positions of lens groups if a same driving method is applied.